329 



ganglion in Amia, Bdellostoma, and Lepidosiren. Platt says (p. 429) 

 that the ascending process bounds the brain laterally, thus forming 

 part of the skull wall. This is probably, in part, an error; the process 

 quite certainly bounding a trigeminal chamber, and not the brain cavity 

 proper. A study of the membranes would decide this. The important 

 point, however, is, that the process is said to form part of the side 

 wall of the skull, and that it lies between the foramina by which the 

 ophthalmicus and maxillo-mandibularis run outward, the one anterior, 

 the other posterior to it. In this relation to these nerves the process 

 corresponds exactly to the pedicle of the alisphenoid of Amia; for it 

 must be remembered that the ophthalmicus trigemini of Necturus, as 

 also that same nerve of the tadpole, is represented, in Amia, by the 

 radix profundus and not by the ramus ophthalmicus trigemini. 



We thus have in Necturus, an amphibian in which the trigeminal 

 ganglion is extracranial, a process, said to be a part of the quadrate 

 that is apparently the homologue of a part of the skull of Amia, a 

 fish in which the trigeminal ganglion is intracranial. The so-called 

 process of the quadrate of the one would seem, from Platt's statements, 

 to have been actually incorporated in the skull of the other, and this 

 is apparently Wiedersheim's interpretation of the facts, for he says 

 (28, p. 389) that the process, because of its relations to the branches 

 of the trigeminus, is "mit vollem Recht mit einem Theil der Ala magna 

 der höheren und höchsten Wirbeltiere zu parallelisiren". Wieders- 

 heim furthermore (p. 376) considers the process as the homologue of 

 the bar of cartilage that, in many Elasmobranchs, separates the two tri- 

 geminal foramina. In Rana, on the contrary, the process seems to 

 simply disintegrate, and so wholly disappear; for Gaupp (10, p. 335) 

 says of it, in his third stage, that it "jetzt zerstört ist". Gaupp, 

 however, says (p. 289), that "Dicht vor der Ohrkapsel ist jedem 

 Trabekel der Proc. ascendens des Quadratums verbunden (Fig. 1 pr. asc); 

 von der Verbindungsstelle aus erhebt sich eine in sagittaler Richtung 

 ganz schmale Leiste bis zum oberen seitlichen Rand des Schädelcavums : 

 die erste Anlage einer knorpeligen Schädelseitenwand, Unmittelbar 

 vor derselben verläßt der N. oculomotorius, über den Trabekel laufend, 

 den Schädelraum". This little pillar in Rana thus seems to be the 

 exact homologue of the vertical cross bar that, in Necturus, bounds 

 posteriorly the oculomotorius foramen. In Rana, the ascending process 

 connects with the trabecula at the ventral end of this little pillar; 

 while in Necturus the process connects with the so-called dorsal bar 

 of the crista trabeculae slightly behind the dorsal end of the pillar. 

 The process in Rana must, accordingly, have slipped downward from 



